Hyperprolactinemia in association with prolactin-secreting pituitary adenomas is being diagnosed and managed with great frequency. In women, this usually is associated with galactorrhea and amenorrhea. However, the etiology of these adenomas is unknown, and the mechanisms by which increased prolactin concentrations affect the hypothalamic-pituitary-ovarian axis remains to be elucidated definitively. An integrated series of clinical and basic investigative studies in women and laboratory rodents is planned to: 1) study dopaminergic regulation of prolactin secretion in vivo and in vitro; 2) determine the effect of long-term hyperprolactinemia on the turnover rate of tuberoinfundibular dopaminergic neurons; 3) assess prolactin modulation of estradiol feedback in hyperprolactinemic women; 4) assess temporal changes in pituitary and ovarian hormones as prolactin levels increase; 5) study various therapeutic modalities in the clinical management of these adenomas; and 6) explore various etiologic factors in the development of pituitary adenomas in women and experimental animals.